1. Field of the Invention
The present invention relates to an optical coupling device, a method of producing an optical coupling device, and an optical apparatus using the same, and, more particularly, to an optical coupling device to form a compound laser beam having RGB information by using optical fiber, a method of producing an optical coupling device, and an optical apparatus using the same.
This application is based on Korean Patent Application No. 2001-69960 filed on Nov. 10, 2001, the disclosure of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
A projector forms an image by projecting an input image signal onto a screen. The projector is used for a presentation in a meeting room, projection in a cinema, and realization of a home theater. More recently, an LCD (liquid crystal display) is mostly used for a projector, and sometimes a CRT (cathode ray tube) is used.
A flat plate device such as an LCD or a CRT is a representative means for image displaying. A conventional method for realizing a mega screen is to project an image shown on the LCD or the CRT onto a screen, after the image is enlarged by a lens. However, since only the image is enlarged, the picture quality of the image is poor. To solve the above-described problem, a projector having a DMD (digital micro-mirror device) has gradually come into use.
The DMD is a semi-conductive optical switch using a micro-mirror. The micro-mirror controls the reflection of the light in accordance with an input image signal. The DMD uses a digital method, thus the color re-productivity of the image signal is good and the brightness is also high. Moreover, A/D or D/A conversion is not required, so a clear image is realized. In addition, the DMD has no loss in the light generated by a Polaroid filter, and thus high optical output can be obtained.
FIG. 1 is a block diagram showing a basic structure of an image projecting apparatus using a conventional laser. Referring to FIG. 1, the conventional image projecting apparatus (hereinafter referred to as ‘projector’) has a laser beam light source 100, an optical system 110, a light separation unit 120, a light modulation unit 130, a light composition unit 140, and a light scanning unit 150. Light passage of the light source 100 is expressed as one-dotted chain line in FIG. 1.
The light source 100 generates a white light laser beam or laser having the respective colors of red, green and blue. The optical system 110 has a first high reflective mirror 112 for changing the passage of the laser beam generated at the light source 100. The optical system 110 also has a first collimating lens 114 for converting the laser beam to a parallel ray, and a first and a second micro lens, 116 and 118 respectively, for adjusting the magnitude of the parallel ray. The first micro lens 116 with a long focal distance is installed at the front end of the optical system 110 and the second micro lens 118 with a short focal distance is installed at the rear end of the optical system 110.
The laser beam that has been transformed into the parallel ray by passing through the first collimating lens 114 is reduced as much as the magnification rate of the first and the second micro lenses, 116 and 118, as the laser beam passes through the lenses 116 and 118. When the magnitude of the laser beam is reduced, the light can be effectively modulated at an AOM (acousto-optic modulator) 134.
The light separation unit 120 includes a first and a second dichroic mirrors 122 and 124, and a second high reflective mirror 126. The light separation unit 120 separates the laser beam incident from the first and the second micro lenses 116 and 118 into a monochromatic light such as red, green and blue. The first dichroic mirror 122 reflects over 99% of blue light and transmits red and green light. The second dichroic mirror 124 reflects over 99% of green light and transmits red light. The second high reflective mirror 126 reflects red light. If an individual laser beam with respect to the monochromatic light such as red, green and blue is generated at the light source 100, then the light separation unit 120 can be excluded.
A focusing lens 132 is installed at a front end of the light modulation unit 130. The focusing lens 132 collimates the laser beam separated into three monochromatic lights at the light modulation unit 130. The light modulation unit 130 uses the same modulator with the AOM 134. The AOM 134 processes signals quickly when the diameter of the passing through laser beam is small. In other words, the focusing lens 132 collimates the laser beam so that the AOM 134 can effectively process the optical signal.
The light composition unit 140 has a second collimating lens 142, a fourth and a fifth dichroic mirrors 144 and 146, and a third high reflective mirror 148. The second collimating lens 142 restores the laser beam that has been optically modulated at the AOM 134 to a laser beam of the initial parallel ray. The fourth and the fifth dichroic mirrors 144 and 146 compound the modulated red, green, and blue light into a white light laser beam. The third high reflective mirror 148 changes the light passage of monochromatic light.
The light scanning unit 150 scans the compounded laser beam horizontally and vertically. The scanned laser beam forms an image on the screen 170 after passing through a projection lens 160. The projection lens 160 forms a clear image by enlarging the laser beam with image information.
However, the dichroic mirror used to form a compound of the separated monochromatic light should be arranged accurately and exactly to transmit the laser beam. In addition, the dichroic mirror takes a lot of space in a projector, thus it is difficult to make the projector small.
Moreover, the dichroic mirror has been used to selectively transmit or reflect the laser beam when the wavelength of the laser beam is different. Yet, when the wavelength of the laser beam is the same, a more complicated structure was required. To form a compound laser beam having the same wavelength, a polarized light device is used. The polarized light device is a device to selectively transmit or reflect vertical polarized light and horizontal polarized light. When a laser beam without polarized light is projected, the polarized light device requires a complicated structure such as a polarizer to polarize the laser beam and a polarization rotation device to rotate the polarized light.